1. Field of the Invention
The present invention relates to a battery pack with which it is possible to enhance productivity of a welding work.
2. Description of the Related Art
A battery pack includes a plurality of cylindrical battery cells, electrode tabs for electrically connecting terminals of the battery cells arranged in a certain pattern, a lower case for containing the battery cells electrically connected through the electrode tabs, and an upper cover for covering the lower case containing the battery cells therein, and is detachably attached to a body of an electronic apparatus, to be used as a power source for the electronic apparatus (refer to Japanese Patent Laid-Open No. 2003-257388).
In the battery packs according to the related art, in the case of spot welding a nickel electrode tab to the battery cell, the non-effective shunt current which flows directly from a welding electrode on one side to a welding electrode on the other side through the electrode tab without flowing through the welding spot and which therefore does not contribute to the welding intended has been suppressed by providing a welding slit such as to elongate the non-effective shunt current path. Besides, the welding slit has functioned also as a register mark for position matching between the electrode tab and a battery cell terminal and for applying the welding electrodes at the time of spot welding.
In such a battery pack, however, in the case of spot welding a copper material electrode tab, the electrical resistivity of copper is very low so that the magnitude of the non-effective shunt current would not materially be changed even when the non-effective shunt current path is elongated by providing a welding slit. Besides, in the case of a copper material electrode tab, a comparison between the mean value of weld strength in the presence of a welding slit and that in the absence of the welding slit has revealed that a higher weld strength is obtained when the welding slit is absent.
However, in the battery pack in which the welding slit is absent, there is no register mark to be used for position matching between the electrode tab and the battery cell terminal and for applying the welding electrodes at the time of spot welding. Therefore, it is difficult to perform welding accurately at the desired position, and the productivity of the welding operation may be worsened.